1. Field of Invention
The invention relates to a polymer energy absorber for motor vehicles which absorbs the kinetic energy released during collisions between motor vehicles and purposely discharges this energy. For this, the polymer absorber is installed in bumper systems and/or bumper arrangements of motor vehicles.
2. Related Art
Prior art discloses different types of energy absorbers which are presently used in the front and/or rear bumper areas of motor vehicles. These energy absorbers have different energy absorption capacities, owing to differences in material and design, as well as differences in the energy-absorption behavior for crash speeds in the typical range of 5 to 15 km/h. As a result of the spaces available for installing energy absorbers in the front and rear motor vehicle region, motor vehicle manufacturers prefer systems having an optimum force-distance characteristic for absorbing kinetic energy at the moment of collision, starting with an initially steep force increase with continuing energy absorption over time, which leads to a constant force level, so that the integral ∫F*ds reaches a maximum value for the force-distance characteristic curve. Reversible and irreversible energy absorber systems for motor vehicles are described in prior art. Hydraulic damping elements are one example of reversible energy absorbers which show a differing response behavior during crashes, depending on the medium used. These hydraulic damping elements have a complex technical design and their weight does not meet the requirements of present-day motor vehicle manufacturers. With respect to the irreversible effect, arrangements consisting of plastically deformable metal elements, e.g. hollow profiles with metal foam (aluminum foam), are known for use as motor vehicle energy absorbers, wherein the energy absorption behavior is mainly determined by the density of the metal foam filler. The production of these irreversible energy absorbers is expensive and involved.
In this connection, prior art also discloses systems combining reversible and irreversible energy absorber elements.
Furthermore known are different types of energy absorbers for motor vehicles which have a differing energy-absorption capacity and are used in a bumper system between the frame side rail and the bumper support in the form of so-called crash boxes or type-damage prevention devices. Besides the bumper support, the crash boxes also absorb crash energy and are irreversibly changed by the deformation. These energy absorbers function to protect the vehicle structure and discharge the crash energy during a collision for speeds up to 15 km/h.
Reference DE 2509265 C2 discloses the use of honeycomb-type deformation elements of plastic or metal which are attached to the bumper. These deformation elements are installed in longitudinal direction of the vehicle and absorb the peak force generated during a crash situation with the aid of the honeycomb structure, so as to dissipate the energy. The technical production of the honeycomb structure in the different types of materials as well as the connection technology are a disadvantage of this design, particularly when using polymer materials, because it results in high production costs and a less secure connection to the receiving elements in the bumper unit of future motor vehicles, given the predetermined installation situation.
Reference DE 3833048 C2 discloses a different energy-absorbing element for the dynamic absorption of crash energy during a vehicle collision phase. This arrangement consists of profile-extruded crash tubes of a composite fiber material with a matrix material from the group of epoxy resins, phenol resins, or vinyl ester resins, wherein these tubes are combined form-locking and coaxial to each other with the vehicle chassis. The disadvantage of this arrangement lies in the reduced force absorption if the vehicle is impact-stressed in vehicle longitudinal direction because of the spatial arrangement of the crash tubes.
Reference DE 4401805 A1 discloses crash dampers with speed-dependent energy conversion. These crash dampers contain fluid-filled pressure chambers for the energy conversion which deform the fluid-filled crash damping elements in longitudinal direction during a vehicle collision and effect an energy dissipation through the compression recovery effect of the selected fluid. The disadvantage of this design lies in the weight of the fluid-filled crash dampers.
A reversible deformation element is described in reference DE 10015294 C2 which discloses a device for absorbing impact energy by means of a tubular sleeve which is provided with an elastic collar that encloses the tube and is composed of a shape-memory alloy and which acts based on the physical memory effect. In the event of an impact, the collar fitted around the outside is expanded in radial direction and the material memory effect then counteracts the collar expansion with a time delay because of the shape-memory alloy characteristic, so that the deformation energy is dissipated slower. The radial and time-delayed energy absorption on the whole results in a lower response behavior of the energy absorber unit during a crash which, combined with the high material costs for the shape-memory alloy, does not meet the future requirements of motor vehicle manufacturers.
A bumper for motor vehicles is furthermore disclosed in reference DE 3232940 C2 which consists of a section that is rigidly attached to the vehicle and is provided with rigid support elements and bent end regions on the side, wherein an undulating plate spring is installed in front of this section. The plate spring and support unit form a single unit made of plastic.
Reference DE 19806541 A1 furthermore discloses a bumper system containing synthetic foam layers with different densities, wherein the energy absorption behavior is realized on two force levels, meaning it transfers an impact resulting from a crash to two different energy absorption levels.
In addition to the aforementioned disadvantages in prior art, the energy absorbers used so far in motor vehicles display an irregular energy absorption behavior, combined with a lower average energy absorption which results in a time delay in the force-distance behavior and, on the whole, negatively influences the response behavior of the energy absorbing unit. Also proposed are energy-absorbing systems for motor vehicles which do not meet the weight requirements of future motor vehicle generations.
Future technical requirements for energy absorbers and energy systems used in motor vehicles must meet the following factors:
high efficiency of the system in the event of a collision;
increasingly smaller installation space;
high reproducibility of the energy conversion;
easy assembly for a replacement or exchange;
stability to climatic influences and
recycling ability.